The invention relates to a device for producing milk froth for cappuccino. More particularly, the present invention relates to a device for producing milk froth for cappuccino, having a nozzle arrangement that is disposed downstream of a steam pipe and that has a vacuum chamber into which a milk supply line terminates, an air conduit connected to the milk supply line upstream of the vacuum chamber, an emulsifying chamber, having a chamber wall, a floor with a central, flow-diverting protrusion and an outlet, disposed downstream of the vacuum chamber, and a settling segment adjoining the outlet.
In a known device of this type for producing a creamy steam-milk-air emulsion for preparing cappuccino, a milk supply line, which has an air opening that is- connected to the atmosphere (U.S. Pat. No. 5,265,519), terminates into a vacuum chamber disposed downstream of a steam pipe having a nozzle. The steam-milk-air mixture produced in the vacuum chamber flows out of the vacuum chamber and into an emulsifying chamber having a closed floor with an essentially conical protrusion. The mixture flowing out of the vacuum chamber, against the central protrusion on the floor of the emulsifying chamber, is divided by the protrusion and reshaped into a new, large-surface mixture flow that impacts the floor of the side wall of the emulsifying chamber and is intended to mix thoroughly with a portion of the mixture already present in the emulsifying chamber to form a good emulsion. This process is supposed to produce a creamy mixture of fine froth that exits through a side opening of the emulsifying chamber and, from there, can flow into a further, cylindrical chamber located to the side of the emulsifying chamber. There, the emulsion settles while excess steam can escape through an upper opening of the additional chamber. This device has yet to achieve its objectives.
For more thoroughly premixing the milk suctioned into the vacuum chamber with air, it is already known to provide a premixing chamber between the vacuum chamber and the milk supply line, with the air conduit terminating into the premixing chamber (EP 0 858 757 A1). While this arrangement produces an extensively homogeneous steam-milk-air mixture in the vacuum chamber, the mixture can still be too large-pored.
Also known from the state of the technology is a device for frothing and heating liquids such as milk or the like. This device is equipped with longitudinal conduits for suctioning froth-producing air around a settling chamber having a relatively large cross ,section and a long length (EP 0 813 834 A1). In this device, first only the suctioned milk is mixed with steam in the vacuum chamber for pre-frothing. For producing the desired froth, the mixture is conducted into an acceleration segment that adjoins the vacuum chamber downstream, and is provided with openings that are connected to the air-conducting longitudinal conduits. The milk and froth are allowed to settle, and be homogeneously distributed, in the cylindrical chamber having the relatively large diameter and long length. This setup does not automatically achieve the desired fine-pore quality desired in many cases, however.
In a similar device, a second nozzle arrangement adjoins the vacuum chamber of the first nozzle arrangement. The second arrangement has air-intake openings that are more directly connected to the atmosphere than the openings connected via longitudinal conduits in the aforementioned arrangement (EP 0344 859 B1). In the second nozzle arrangement, air is suctioned and added to the milk to produce froth, which is then suctioned with the first nozzle arrangement. The froth flows out of a chamber that adjoins the second nozzle arrangement, the chamber having a relatively large diameter and long length, through lower, notably lateral, openings in the chamber, and consequently settles and is uniformly distributed. The floor of this chamber is shaped so as to prevent the froth from exiting directly at a high speed. For this purpose, the floor has a rounded protrusion. The floor has individual drip openings near the edge. This device also does not attain the desired fine-pored, homogeneously emulsified steam-milk-air mixture.
It is the object of the present invention to create a device for producing milk froth for cappuccino, with which the milk froth is homogeneously emulsified and fine-pored.
The above object generally is achieved according to the present invention with a device of the generic type described at the outset, wherein the emulsifying chamber, which is formed without separate air inlets, has at least two free cross sections that widen step-wise in the primary flow direction, and the central, flow-diverting protrusion is formed as a flow trap that surrounds the outlet in the floor such that the protrusion diverts a mixture flowing essentially in the primary flow direction essentially to a direction counter to the primary flow direction. Also disclosed are variations of the basic solution. The basic solution and vacations thereof are based on the common principle that the steam-milk-air mixture formed in the vacuum chamber after the premixing of the milk with air is mixed intensively again, and swirled, in the emulsifying chamber The mixture remains in the emulsifying chamber as long as possible, where it is emulsified into a fine-pored mixture due to the continuous flow of steam energy.
According to the basic solution, the cross sections of the emulsifying chamber, which increase step-wise in the downstream direction, strongly swirl the steam-milk-air mixture in the emulsifying chamber. The central, flow-diverting protrusion around the outlet in the floor of the emulsifying chamber, which is embodied as a flow trap, lengthens the time spent by the steam-milk-air mixture in the emulsifying chamber by diverting the mixture, which impacts the trap essentially in the primary flow direction, essentially counter to the primary flow direction. The primary flow direction is defined by the nozzle arrangement of the vacuum chamber, which changes over into the emulsifying chamber downstream. The settling segment adjoins this specially-designed emulsifying chamber by way of an outlet in the floor of the emulsifying chamber. The settling segment having the outlet can be embodied simply as a throughgoing bore.
An additional advantage of this device is its compact design.
For the basic inventive embodiment of the emulsifying chamber, it suffices to provide two segments that follow one after the other in the primary flow direction, with the first segment widening step-wise relative to an outlet of the vacuum chamber, and the second segment having a cross section that is widened, step-wise, relative to the first segment, in connection with the flow trap in the floor, i.e., the downstream end of the emulsifying chamber.
A significantly better option for attaining the desired fine-pored emulsion, according to a modification of the basic embodiment, is for the emulsion chamber to comprise three segments, whose cross sections widen, step-wise, relative to the cross section of the outlet of the vacuum chamber or the upstream adjacent segment. The flow trap is provided it the floor of the emulsifying chamber in this case as well.
According to a feature of the invention, the flow trap is embodied or formed as a blind ring having an annular trough that is open counter to the primary flow direction of the steam-milk-air mixture. The trough is embodied and oriented such that it diverts the steam-milk-air mixture, which impacts it essentially in the primary flow direction, essentially counter to the primary flow direction. This swirls the mixture again and keeps it in the emulsifying chamber longer.
In a further modification of the basic invention, a flow-diverting unit is disposed in the emulsifying chamber, at a distance from the floor. This unit is embodied such that the flow of the steam-milk-air mixture is diverted essentially counter to its primary flow direction. This flow diversion, again, effects a desired swirling of the flowing mixture in addition to the swirling effected by the flow trap that is always provided in the floor of the emulsifying chamber in accordance with the invention.
According to a preferred feature of the last mentioned embodiment, the flow-diverting unit call advantageously be embodied with an open, annular trough that surrounds a central, essentially conical protrusion. This trough can be embodied similarly to, but flatter than, the annular, open trough of the flow trap in the floor.
According to a feature of the invention, the flow-diverting unit is advantageously held in the emulsifying chamber, at a distance from the inside wall of the chamber, by radial ribs, so the flow can occur in the primary flow direction in the region of the inside wall.
In a variation of the device of the invention, the emulsifying chamber has diaphragms at the steps between its segments, with the diaphragms additionally narrowing the adjacent, smaller cross section. These diaphragms or narrow points form pronounced, turbulence-inducing edges that effect an even more vigorous swirling of the steam-milk-air mixture than the steps of the cross sections themselves.
Particularly for better cleaning, but also for the uncomplicated production of the emulsifying chamber and the adjacent regions, the emulsifying chamber has individual elements, which are cylindrical on the outside and are formed out with at least one of the stepped cross sections on the inside, and are held together by a common sleeve. All of the elements are disposed concentrically in the sleeve, which has a smooth outside surface.
According to a feature of the invention, the elements of the emulsifying chamber can comprise a half-hard synthetic material, notably chloroprene caoutchouc (brand name xe2x80x9cNeoprenxe2x80x9d). This synthetic material also has a sufficient dimensional stability when exposed to steam.
In accordance with a combination feature of the device of the invention, a premixing chamber is preferably disposed between the vacuum chamber and the milk supply line; the air conduit terminates into this chamber. This assures the homogeneous air distribution of the emulsion, namely the entry of a thoroughly premixed milk-air mixture into the vacuum chamber before steam is added to the mixture and the additional swirling takes place in the emulsifying chamber.
Three variations of the invention are explained below by way of exemplary embodiments, with reference to the four drawing figures.